Useful substances have often poor solubility in water in the fields of pharmaceutical products, veterinary pharmaceutical products, quasi-drugs, cosmetic products, food products, agricultural chemicals, and the like. This restricts the use of useful substances. Thus, it has been desired to develop a method for improving the solubility of poorly-soluble useful substances.
Under such circumstances, the present inventors had proposed a method for improving the solubility of a poorly-soluble substance, wherein the surface of the poorly-soluble substance particle is coated by applying mechanical energy to allow the microparticles of a calcium compound such as calcium phosphate or calcium carbonate to penetrate into the poorly-soluble substance particle to improve the solubility (see Patent Document 1).